Monday, 19 March 2012

Sperm may feel the weight of extra pounds: study

Heavy men are more likely than their normal-weight peers to have low
sperm counts or no sperm production at all, suggests a new report.

The
review of past studies can't prove that overweight or obese men will
have more trouble fathering a child. But researchers said that how many
sperm men make is one of the key ways doctors measure their fertility.

"In
general you expect that men with lower sperm counts will have a greater
frequency of difficulty conceiving than men with higher sperm counts,
but it's not completely straightforward," said Dr. Jorge Chavarro, from
the Harvard School of Public Health, part of the collaborative group
that put out the study.

How well
sperm move, their shape and the quality of DNA they carry matter too,
Chavarro said -- but previous studies have suggested some of those
measures of sperm quality may be affected by obesity as well. For the
new analysis, French researchers combined data from 14 studies that
compared sperm count in samples of ejaculate from normal weight,
overweight and obese men, as well as data from their own infertility
center.

About one-quarter of the
combined 10,000 men had a low sperm count. In another analysis, just
over 250 out of almost 7,000 men had no sperm in their ejaculate at all.

Dr.
Sebastien Czernichow, from the Ambroise Pare Hospital,
Boulogne-Billancourt, and colleagues calculated that compared to
normal-weight men, overweight men were 11 percent more likely to have a
low sperm count and 39 percent more likely to have no sperm -- though
it's possible the second finding was due to chance.
Obese
men, on the other hand, were 42 percent more likely to have a low sperm
count than their normal-weight peers and 81 percent more likely to have
sperm-free ejaculate, the researchers reported in the Archives of
Internal Medicine.

They proposed
a number of different theories for the findings, including that male
hormones may be converted into estrogen in fat tissue, affecting
sperm-making down the line, or that more fat in the hips and stomach
could make the scrotum too hot.

The
results don't prove that overweight and obese men will have more
fertility trouble -- although you wouldn't expect men who have no sperm
at all to be fertile, Chavarro said. And it's possible that the obesity
itself isn't to blame; rather, in some men, an underlying health
condition causes them to gain weight and affects their sperm, said Dr.
Stephen Winters, Professor of Medicine and Chief of the Division of
Endocrinology, Metabolism and Diabetes at the University of Louisville.

Because
of that, researchers can't say for sure whether heavy men could boost
their sperm production by losing weight. Czernichow told Reuters Health
in an email that losing weight improves fertility in women, but that
there's not much data in men -- though small case reports have
suggested weight-loss surgery may actually have a negative effect on
sperm.

The findings jibe with a
study from late last year which found that being overweight was tied to
a lower sperm concentration and lower motility -- how well sperm swam
(see Reuters Health story of November 18, 2011).

The
current report "is not conclusive, and the risks are not huge,"
Winters, who wasn't involved in the research, told Reuters Health. But
fertility trouble, he added, "is there among the health risks of
obesity."

"This appears to be
yet another health outcome for which maintaining a healthy weight
appears to be important," Chavarro told Reuters Health.

"It's
not only about your cardiovascular disease risk, it's not only about
diabetes and some forms of cancer. Obesity also seems to affect
outcomes that may be manifested in younger men."